During the fabrication of integrated circuits, ICs, a plurality of IC chips are fabricated on a semiconductor wafer. After singulation, the individual chips are packaging into IC components. To ensure good functions and designed performance, there are several testing steps involved before sending to the customers.
Testing of IC chips on a wafer before singulation is called chip probing or wafer sorting. Since the design of IC chips becomes more complicated, therefore, through chip probing or wafer sorting, the yield of the fabricated wafer can be determined then feed back to IC fab for process improvement.
An IC tester for chip probing or wafer sorting has a test head on which a probe card is installed as a signal transmitting medium between the tester and the wafer under test.
As revealed in U.S. Pat. No. 5,974,662, a conventional interposer of a modular probe card comprises a substrate and a plurality of resilient contact structures where the resilient contact structures are curved probes formed on the top surface and on the bottom surface of the substrate. Each resilient contact structure has a soft core overcoated with a hard material. The soft cores are used to form the desired shape and the hard material is formed on exposed surfaces of the cores. When the interposer is disposed between the probe head and the printed circuit board of a probe card, the resilient contact structures on the interposer will make electrical connections between the probe head and the printed circuit board. Since the resilient contact structures are curved probes disposed on the substrate, it is very difficult to control contact tips of all the curved probes. Moreover, when the interposer is disposed between the probe head and the printed circuit board, the curved probes can be easily damaged and deformed so that the interposer can not be reused.
Furthermore, another conventional interposer for modular probe card as revealed in R.O.C. Taiwan patent publication No. 493,756, a universal probe card comprises an interposer, a printed circuit board, and a probe head where one surface of the interposer has a plurality of first contact pins and the other surface a plurality of second contact pins. The pitches between the first contact pins are the same, so as the pitches between the second contact pins. The printed circuit board has testing circuits fabricated in it which is interchangeable. One surface of the printed circuit board is electrically connected to the test head of a tester and the other surface has a plurality of first through holes where the pitches of the first through holes are the same as the first contact pins on the interposer so that the first contact pins of the interposer can contact with the corresponding first through holes. The probe head has a plurality of probes fabricated on one surface and the second through holes on the other surface where the pitches of the second through holes is the same as the second contact pins of the interposer so that the second contact pins of the interposer can contact with the corresponding second through holes. However, due to different thermal expansion coefficients, CTEs, between the printed circuit board and the interposer, the pitches of the plurality of the first through holes on the printed circuit board will be changed due to temperature gradients. Therefore, the plurality of the first contact pins on the interposer can not fully contact with the plurality of the first through holes on the printed circuit board leading to electrical connection failure.